Most of the heat transfer through something like rock wool or anything with an air pocket is though radiation. There is little conduction due to the long convoluted, and extremely narrow fibres that form the material and the low conduction coefficients for gases. There is no convection due to the lack of fluid movement. It appears to me that the layer in the Triso are of a similar open cell foam type material. The foil will act as a vapour barrier and anti convection agent, while also having an extremely low conductivity and acting as a radiation barrier. Any heat that gets through one layer is further trapped in the next layer by the foil, giving a step change in temperature profile through the material.

The 0.0057 value I quoted was obtained by independant testing as far as I could ascertain. I doubt that the developers of Triso have gone to the expense of a multi-layered product (and Triso is v expensive) if there is no purpose to it.

I came across it when it was recommended as a space saving insulator that would maintain the insulation levels for building regs. I was going to use it in my fridge installation, but then I found I wasn't that tight on space in the new boat and the cost put me off.